1. Field of the Invention
The present invention relates to a wireless receiver for use with an electroacoustic transducer such as a loudspeaker, for example.
2. Description of the Prior Art
Some small or simple loudspeakers, called active loudspeakers, include a power amplifier powered by a battery and housed in a loudspeaker enclosure.
The circuit arrangement of one such active loudspeaker is illustrated in FIG. 1 of the accompanying drawings. The illustrated circuit components are all housed in a loudspeaker enclosure.
The loudspeaker has an input terminal 1 supplied with an audio signal SA, a power amplifier 2 for amplifying the audio signal SA, and a loudspeaker unit 3 for converting the audio signal SA into sounds. A power supply battery 5 comprises four series-connected dry cells, for example. The battery 5 is connected to a power line of the power amplifier 2 through a power switch 6.
A detector 8 is connected to the input terminal 1 for detecting whether there is an audio signal SA supplied to the input terminal 1 or not. A detected signal from the detector 8 is supplied through a driver 9 as a control signal to the power switch 6. The voltage from the battery 5 is applied as an operating voltage to the detector 8 and the driver 9 at all times.
When an audio signal SA is supplied to the input terminal 1, it is detected by the detector 8, which applies a detected signal SD to the driver 9, thereby turning on the switch 6. The voltage of the battery 5 is therefore applied through the switch 6 as an operating voltage to the power amplifier 2. Accordingly, the audio signal SA supplied to the input terminal 1 is amplified by the power amplifier 2 and supplied to the loudspeaker unit 3.
When the audio signal SA is no longer supplied to the input terminal 1, no detected signal SD is produced by the detector 8, and hence the switch 6 is turned off.
Since certain poor frequency characteristics of the loudspeaker unit 3 can be compensated for by the power amplifier 2, the loudspeaker can radiate high-quality reproduced sounds even through it is small in size.
As the power amplifier 2 is automatically energized or de-energized depending on whether there is supplied an audio signal SA or not, the user of the loudspeaker is not required to turn on and off the power switch.
The current consumed by the detector 8 and the driver 9 can be sufficiently minimized, and the power amplifier 2 is automatically turned off when the audio signal SA is no longer supplied. Consequently, any wasteful consumption of the battery 5, which would otherwise be the case if the user forgot to turn off the power switch, is avoided.
Inasmuch as the battery 5 is housed in the loudspeaker, no external power supply cable is needed. An audio signal from a headphone stereo set can easily be reproduced by the loudspeaker.
However, since an audio signal SA has to be supplied through the input terminal 1 to the power amplifier 2, a signal cable needs to be connected to the input terminal 1.
One solution is to supply an audio signal SA to the loudspeaker through wireless signal transmission.
FIGS. 2 and 3 show conventional loudspeakers with wireless signal reception capabilities.
In FIG. 2, an audio signal SA is supplied through infrared radiation. More specifically, when an audio signal transmitter (not shown) is turned on, an infrared radiation LT which is modulated by a remote control signal SC is emitted by the audio signal transmitter. The emitted infrared radiation LT is detected by a photodiode 11 and converted into a signal ST, which is then applied to a decoder 14. The decoder 14 decodes the signal ST back into the remote control signal SC, which is applied to the driver 9 to turn on the switch 6.
Therefore, the operating voltage is now applied to a signal receiver 12 and the power amplifier 2 by the battery 5.
Then, the audio signal transmitter transmits an infrared radiation LT that is modulated by an audio signal SA. The infrared radiation LT is detected by the photodiode 11 and converted into a signal ST, which is then supplied to the receiver 12. The receiver 12 converts the signal ST into the audio signal SA. The audio signal SA is then supplied through the power amplifier 2 to the loudspeaker unit 3.
The loudspeaker shown in FIG. 2 does not require either an external signal cable or an external power supply cable. The loudspeaker may be placed in any position where the user wants it to reproduce sounds, and the user can readily enjoy reproduced sounds from the loudspeaker.
In FIG. 3, when a switch 16 is depressed, a timer 17 is triggered by a signal from the switch 16, and the switch 6 remains turned on for a certain period of time by an output signal from the timer 17.
Therefore, when the switch 16 is depressed and the audio signal transmitter emits an infrared radiation LT modulated by an audio signal SA, the audio signal SA is reproduced as sounds by the loudspeaker unit 3.
The loudspeaker shown in FIG. 3 also requires no external signal cable nor no external power supply cable. The loudspeaker may be placed anywhere, and the user can readily enjoy reproduced sounds from the loudspeaker.
With the circuit arrangement shown in FIG. 2, it is necessary for the user to turn on and off the power supply of the audio signal transmitter. If the user forgets to turn on or off the audio signal transmitter, the loudspeaker will not reproduce sounds or will cause a wasteful consumption of the battery 5.
The decoder 14 needs to be energized at all times. However, it is not practical to energize the decoder 14 at all times because it consumes a large current.
The switch 16 of the loudspeaker shown in FIG. 7 needs to be manually operated by the user. Even while sounds are being reproduced by the loudspeaker, when a preset period of time elapses after the switch 16 is depressed, the switch 16 is forcibly turned off by the timer 17. Therefore, the sound reproduction may be interrupted undesirably.